Warpage control of array packaging

ABSTRACT

During the curing process of the package strips, especially during post encapsulant cure (PEC), undesirable warpage of package strips occurs. A carrier having angled lands and side-insertion clamp structures with angled clamp fins may be used to control this cure-induced warpage of package strips during PEC. In one embodiment, the angled lands and angled side-insertions clamps are used to clamp the edges of the package strip in order to introduce an intentional deformation which counters warpage which occurs during PEC. The angled lands and side-insertion clamps may be at any angle (fixed or adjustable). The side-insertion clamps may be inserted before or after insertion of the package strips into the carrier. Once the package strips are in the carrier and resting on the angled lands, a force may be applied to the side-insertion clamps to clamp the edges of the package strips between a clamp fin and an angled land.

FIELD OF THE INVENTION

The present invention relates generally to semiconductor packaging, andmore specifically, to warpage control of array packaging.

RELATED ART

Single array and multi-array packaging techniques are currently usedtoday to reduce processing time and cost. FIG. 1 illustrates a packagestrip 10 as known in the art. Package strip 10, as illustrated in FIG.1, is a multi-array package (MAP) having a plurality of devices likedevices 16, 17, and 18 in the form of an array overlying a packagesubstrate 12. Alternatively, package strip 10 may be a single arraypackage. Package substrate 12 may be a laminate package substrate,formed as known in the art, and may include any number of laminatelayers. Each device 16–18 includes an integrated circuit die physicallyand electrically connected to package substrate 12. For example, theintegrated circuit die may be physically attached to the packagesubstrate using an adhesive, and may be electrically coupled to thepackage substrate via wire bonds, as known in the art today. Afterattaching and electrically connecting the integrated circuit die to thepackage substrate, an encapsulant 14 may be formed over the integratedcircuit dies while leaving a perimeter portion at the edges of packagesubstrate 12. Encapsulant 14 may be any type of encapsulant, such as,for example, a thermal set overmold or a glob. Furthermore, encapsulant14 may encapsulate all devices of strip 10 together, as illustrated inFIG. 1, or may encapsulate groups of devices or single devices of strip10. For example, smaller arrays of devices within strip 10 may beencapsulated together such that encapsulant 14 includes separateencapsulant portions.

FIG. 2 illustrates a cross-sectional view of packaged substrate 12 takenthrough devices 16, 17, and 18. As illustrated in FIG. 2, each device16–18 includes an integrated circuit die 20–22, respectively, attachedto package substrate 12 between two corresponding singulation marks 28.Each of the integrated circuit dies 20–22 are electrically connected topackage substrate 12 via wire bonds 24–26, respectively. Therefore, atsome point later in the process, each of devices 16–18 may be singulatedalong the singulation marks 28. That is, referring back to FIG. 1, eachof the devices may singulated from each other by separating the devicesbetween the dotted lines illustrating the perimeters of the devices. Inone embodiment, singulation is done by punching, cutting, or sawing.

During formation of encapsulant 14, curing is performed to cross-link orharden the encapsulant material. After formation of encapsulant 14,strip 10 may be placed in a carrier for a post encapsulant cure (PEC) inorder to allow the curing process to continue. (Note that whenencapsulant 14 is a thermally set overmold, post encapsulant cure may bereferred to as post mold cure (PMC)). That is, during the PEC, theencapsulant material continues to cross-link or harden to solidify thefinal curing stage of the encapsulant material. FIG. 3 illustrates aconventional carrier 30, used today in the art, having slots such asslots 32 and 36 into which package strips 31 and 33 (each of which maybe a package strip such as package strip 10) may be placed. Therefore,the curing of package strips 31 and 33 continues within carrier 30. Thepackage strips slide into slots 32 and 36 and rest atop horizontal lands34 and 38, respectively.

Generally, note that the PEC (while in the carrier) is substantiallylonger than the curing process performing during the formation of theencapsulant. During the curing process, especially during the PEC incarrier 30, warpage of the package strips occurs. For example, asillustrated in FIG. 3 with package strip 33, warping of the packagestrips occurs which causes problems in later processing. This warpagemay be caused, for example, by the mismatch of coefficients of thermalexpansions (CTEs) of the various components of the package strip such asthe package substrate, encapsulant, and integrated circuit dies. Theamount of warpage is also affected by the size, thickness, and materialsof the encapsulant, package substrate, and integrated circuit die. Thiswarpage causes problems later in manufacturing, and therefore needs tobe minimized.

One attempt at solving this problem today uses a piling technique whereafter encapsulation, the package strips are piled on top of each otherwith a weight or other pressure applied to the top of the pile. However,this does not adequately control warpage during the PEC after piling.Furthermore, the use of piling increases manufacturing time thusreducing line efficiency.

Another attempt at solving this problem today modifies carrier 30 tohave tighter slots. For example, the openings of the slots (such asslots 32 and 36) are reduced; however, sufficient empty space stillexists within the slot opening between the top of a package strip andthe next horizontal land above it to allow the strips to slide in anout. That is, the package strip is not in physical contact with the topof the next horizontal land before PEC. However, this does noteffectively reduce warpage. Furthermore, any warpage which does occurmay prevent the strip from being able to be removed from the carrier dueto the warped strip being stuck in the tight slots.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and not limitedby the accompanying figures, in which like references indicate similarelements, and in which:

FIG. 1 illustrates a top-down view of a package strip as known in theart;

FIG. 2 illustrates a cross-sectional view of the package strip of FIG.1;

FIG. 3 illustrates an end view of a package strip carrier as known inthe art today;

FIG. 4 illustrates an end view of a carrier assembly havingside-insertion clamp structures according to one embodiment of thepresent invention;

FIG. 5 illustrates the carrier assembly of FIG. 4 after application of aclamping force;

FIG. 6 illustrates a three-dimensional view of a portion of the carrierassembly of FIGS. 4 and 5; and

FIG. 7 illustrates a three-dimensional view of a side-insertion clampstructure such as those illustrated in FIGS. 4 and 5.

Skilled artisans appreciate that elements in the figures are illustratedfor simplicity and clarity and have not necessarily been drawn to scale.For example, the dimensions of some of the elements in the figures maybe exaggerated relative to other elements to help improve theunderstanding of the embodiments of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

As described above, the curing process, especially during PEC, causesundesirable warpage of package strips, such as package strip 10 ofFIG. 1. As will be described herein, a carrier having angled lands andside-insertion clamp structures may be used to control cure-inducedwarpage of package strips during PEC. Therefore, the embodimentsdescribed herein apply to package strip 10 of FIG. 1. As describedabove, package strip 10 is illustrated as a MAP, but alternatively itmay be a single array package having only one row of devices. Therefore,the embodiments described herein apply to any type of package strip suchas any type of MAP or single array package; however, for ease ofexplanation, the embodiments described herein will be described inreference to package strip 10 of FIG. 1.

FIG. 4 illustrates a carrier assembly 40 including a carrier 42 andside-insertion clamp structures 43 and 44, according to one embodimentof the present invention. Note that carrier 42 includes a plurality ofangled lands such as angled lands 45 and 46 along each inner or interiorsidewall. These angled lands are illustrated as lined up along a dottedline because there are spaces between the angled lands (see, e.g.,spaces 68 of FIG. 6). The angled lands are held together with supportbars (see, e.g., support bars 66 of FIG. 6) extending down the length ofcarrier 42. For example, these bars may exist at the openings of eitherend of carrier 42 and at predetermined spaces along the sides of carrier42. Carrier 42, as illustrated in FIG. 4, is holding two package strips,package strips 52 and 54, resting on corresponding angled lands. Forexample, package strip 54 is resting on angled lands 45 and 46. Notethat at this point, each of package arrays 52 and 54 have hadencapsulants formed thereon and are substantially horizontal (inreference to the tops and bottoms of carrier 42) when placed in carrier42. Note that carrier 42 may be of any size and may include any numberof angled lands to support any number of package strips. Therefore,although only two package strips are illustrated, carrier 42 may includeany number of package strips for which there are angled lands available.

As illustrated in FIG. 4, each of the angled lands, such as angled land45, is as at an angle 47 as measured from a horizontal axis, where thehorizontal axis of FIG. 4 is substantially parallel to package strips 52and 54 and the tops and bottom of carrier 42. Angle 47 may be any angle,including 0 degrees. In one embodiment, angle 47 is fixed such that eachof the angled lands of carrier 42 are fixed at a same angle.Alternatively, the angled lands of carrier 42 may be designed such thatangle 47 can be adjusted as desired. For example, the angled lands maybe attached with rotating hinges to the sidewalls of carrier 42. In oneembodiment, angle 47 is at a non-right angle to the sidewall of carrier42. Also, in one embodiment, angle 47 is at a non-right angle to thepackage strips 52 and 54. Note that in one embodiment, all of the angledlands are at a same angle with respect to the sidewalls of carrier 42.

Also illustrated in FIG. 4 are side-insertion clamp structures 43 and44, where each of the clamp structures includes clamping fins (or clampfins) such as clamping fins 49 and 50, respectively (supported by clampbars, as will be described in reference to FIG. 7 below). The clampingfins, such as clamping fins 49 and 50, are inserted into the spacesbetween the angled lands of carrier 42. They are inserted such that eachclamping fin is close to the angled land above the clamping fin, thusleaving sufficient space for package strips 52 and 54 resting upon theangled lands. Therefore, there are generally as many clamping fins asthere are angled lands. Also, the clamping fins are at substantially asame angle with respect to the horizontal axis as the angled lands(where this angle may be fixed or adjustable). That is, the clampingfins and angled lands are substantially parallel. Note that in oneembodiment, clamp structures 43 and 44 may be present as illustrated inFIG. 4 prior to insertion of package strips such as package strips 52and 54 into carrier 42, or may be inserted after insertion of thepackage strips.

After the clamp structures and package strips are in place, asillustrated in FIG. 4, clamp structures 43 and 44 are used to clamp theedges of package strips 52 and 54. In one embodiment, a clamping forceillustrated with arrow 48 is applied to allow clamp structures 43 and 44to clamp the edges. FIG. 5 illustrates carrier assembly 40 and packagestrips 52 and 54 after clamping the edges of package strips 52 and 54where the clamping force constrains package strips 52 and 54 between acorresponding angled land and clamping fin. Therefore, in oneembodiment, upon application of the clamping force, a major surfaceportion of the package substrates (of package strips 52 and 54) near anedge of the package substrates (e.g. a first major surface periphery ofthe package substrates) is engaged with clamping fins disposed at anangle to the major surface.

Due to the angled lands and the angled clamping fins, the clamping ofpackage substrates 52 and 54 results in an initial deformation ofpackage strips 52 and 54. For example, package strips 54 deviates fromthe horizontal axis by a warp distance 56. In one embodiment, packagestrips 52 and 54 are deformed to have a resulting curvature that isdifferent from an at-rest curvature, where the at-rest curvature is acurvature that is present without application of stresses or force topackage strips 52 and 54 but which may already include some degree ofwarpage due, for example, to prior processing steps. In one embodiment,the at-rest curvature corresponds to the curvature that is present priorto deformation (introduced, for example, by clamp structures 43 and 44).In one embodiment, package strips 52 and 54 are deformed to have aconstrained curvature (upon clamping) that is different from an at-restcurvature. The intentional deformation of package strips 52 and 54 maytherefore be used to counter the expected cure-induced warpage due tosubsequent PEC. That is, the clamping by clamp structures 43 and 44 isheld during the PEC in order to counter the warpage. Therefore, duringPEC, package substrates 52 and 54 warp, but this warpage is countered bythe initial deformation held by clamp structures 43 and 44. After PEC,clamp structures 43 and 44 may be released, such that the packagestructures may be removed from carrier 42. In one embodiment, packagestrips 52 and 54 are held in carrier 42 during PEC and are maintained incarrier 42 for a time after PEC before being removed.

Note that in one embodiment, the initial deformation (which may beintroduced by clamping) causes an arc in a first reference direction toprovide stiffness to the package strips to prevent warpage (during, forexample, PEC) in the first direction and in a second reference directionsubstantially orthogonal to the first reference direction.Alternatively, different types and forms of initial deformation may beperformed to counter warpage. Also note that in alternate embodiments,clamping without an initial deformation may also be used to counterwarpage. In this embodiment, the clamping may or may not cause packagestrips 52 and 54 to deform away from their at-rest curvature. Forexample, clamp structures 43 and 44 may be used to constrain the edgesof package strips 52 and 54 at an angle that is substantially orthogonalto the sidewalls of carrier 42 (thus introducing substantially noinitial intentional deformation) where the clamping itself counterswarpage during PEC. Therefore, in this embodiment, package strips 52 and54 may have a constrained curvature upon clamping that is notsubstantially different from an at-rest curvature. Also, as describedabove, the encapsulant of package strips 52 and 54 may be partiallycured prior to clamping, where this partial curing may occur duringformation of the encapsulant or in carrier 42 or both.

The angled lands and clamp fins can be formed at any angle needed suchthat an appropriate amount of deformation is introduced on packagestrips 52 and 54 to counter cure-induced warpage. For example, theangles of the angled lands and clamp fins can be set to counter anexpected cure-induced warpage, where the amount of expected warpage isknown. This cure-induced warpage depends, for example, on variousfactors such as the thickness of the dies, the sizes of the dies, thetype of package, etc. In one embodiment, the angles of the angled landsand clamp fins can be set based on these types of factors. Furthermore,they can be modified as needed based on any changes in these types offactors. In an alternate embodiment, an amount of the PEC warpage of thepackage strips may be measured as guide for applying any clamping force,and the angle of the lands and clamp fins may be selected based on thismeasured warpage. In yet another embodiment, as described above, theangle may be set such that substantially no amount of deformation isintroduced by the clamping.

FIGS. 6 and 7 illustrate three-dimensional views of a carrier and aclamp structure, respectively. FIG. 6 illustrates a portion of a carrier60 (which may correspond, for example, to carrier 42) having angledlands 62 which are at an angle 64 with a horizontal plane, where thehorizontal plane of FIG. 6 is defined as perpendicular to the planedefine by the illustrated sidewall of carrier 60. Note that as describedabove, carrier 60 includes support bars 66 (where, in the illustratedembodiment, support bars 66 also form part of the out edge of carrier60). Note that in alternate embodiments, more or less support bars thanthose illustrated may be used. For example, a support bar may be usedbetween support bars 66 of FIG. 6. Note that as described above, spacessuch as spaces 68, exist between the angled lands which allow forinsertion of a clamp structure. FIG. 7 illustrates a portion of a clampstructure 70 (which may correspond, for example, to either one of clampstructures 43 and 44). Clamp structure 70 includes support or clamp bars72 (as also illustrated in FIGS. 4 and 5) which are used to supportclamp fins 74 at an angle 78, where angle 78 is measured from ahorizontal plane (which is perpendicular to the plane defined by supportbars 72 where, for example, this horizontal plane is parallel to ahorizontal plane defined by dotted lines 76). Clamp bars 72 may belocated on sides of clamp fins as illustrated in FIG. 7, or located atthe ends of the fins. Clamp fins 74 may be inserted into spaces of acarrier (such as spaces 68 of carrier 60). Note that carrier 60 andclamp structure 70 may have many different forms which allow forclamping of package strips. Furthermore, the angles such as angles 78and 64, may be fixed or variable.

Note that the angles of the angled lands and clamp fins described inreference to FIGS. 4 and 5 are illustrated as non-zero with respect tothe horizontal axis of FIG. 4. However, in one embodiment, the angle iszero such that the angled lands and clamp fins are perpendicular to thesidewalls of carrier 42. In this embodiment, clamp structures are usedto clamp the package strips to help counter warping during PEC. In thisembodiment, note that the clamping does not result in an initialdeformation as illustrated in FIG. 5. However, note that in manyembodiments, regardless of what the angle is of the angled lands andclamp fins, after clamping, the edges of the package strips are clampedbetween an angled land and clamp fin and thus in physical contact withboth the angled land and clamp fin which reduces the array warpage.

Note also that in FIGS. 6 and 7, the angled lands (such as angled land62 in FIG. 6) and clamp fins (such as clamp fin 74 in FIG. 7) areillustrated as straight in the longitudinal direction. For example, notethat in FIG. 6, the edge of each angled land 62 that is adjacent to awall of carrier 60 (e.g. attached to support bars 66) is at a constantdistance from the bottom (or top) of carrier 60, and that in FIG. 7, theedge of each clamp fin 74 that is adjacent to support bars 72 is at aconstant distance from the bottom (or top) of support bars 72. However,in alternate embodiments, these angled lands and clamp fins can be madecurved or arched with a curvature counter to the warpage induced in thePEC. For example, a center portion (e.g. between dotted lines 76) ofangled lands 62 and clamp fins 74 may be at a greater distance from thebottom of carrier 60 and support bars 72, respectively, as compared toend portions (located at the front and back openings or portions) ofcarrier 60 and clamp structure 70. Alternatively, angled lands 62 andclamp fins 74 may have any other type of curvature, as desired, tocounter or control warpage. Therefore, in one embodiment, angled lands62 and clamp fins 74 may be both angled and curved.

Note that the clamping of FIGS. 4 and 5 was described in reference to aforce indicated by 48 which is applied in a direction indicated by arrow48. This clamping force can be applied in a variety of different waysusing a variety of different implementations. For example, in oneembodiment, the clamping structures may be pulled down in the directionof arrows 48 and fixed to a fixed point, using, for example, a screw,peg, or other securing mechanisms. Alternatively, the clampingstructures may be pushed down in the direction of arrows 48 and securedto a fixed point, using, for example, a screw, peg, or other securingmechanisms. Therefore, any means of applying a force may be used and anymeans of maintaining that force to allow the clamp structure to remainclamped may be used. For example, the clamping may be performed byapplying a weight or force, by rotating a screw, by setting or releasinga spring, by an actuating level, etc., or by any combination thereof.

Alternate embodiments may use various other ways of achieving theclamping and of achieving an intentional deformation. For example, theedges may be clamped prior to applying a force for inducing an initialdeformation. In this example, the lands and clamp fins may initially beorthogonal (or at some other angle) to the sidewalls of the carrier,where after clamping, the lands and fins may be angled or otherwiseaffected in order to apply a deformation force to the package stripsthat results in the initial deformation (if that initial deformation isdesired). That is, in alternate embodiments, a clamping force may beused such that no initial deformation is introduced. In this case, theclamping force constrains the package strips during PEC to counterwarpage without an initial deformation. Alternatively, intentionaldeformation can be achieved by placing package strips into slots of acarrier, and then squeezing the sides of the carrier to reduce the widthsuch that an intentional deformation is introduced. Forces other thansqueezing may also be used to create and maintain the counter warpage.Also, different forms of clamping fins and clamping structures may beused to clamp the package strips, regardless of whether a deformation isintroduced or not.

In the foregoing specification, the invention has been described withreference to specific embodiments. However, one of ordinary skill in theart appreciates that various modifications and changes can be madewithout departing from the scope of the present invention as set forthin the claims below. Accordingly, the specification and figures are tobe regarded in an illustrative rather than a restrictive sense, and allsuch modifications are intended to be included within the scope ofpresent invention.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any element(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature or element of any or all the claims. As used herein, the terms“comprises,” “comprising,” or any other variation thereof, are intendedto cover a non-exclusive inclusion, such that a process, method,article, or apparatus that comprises a list of elements does not includeonly those elements but may include other elements not expressly listedor inherent to such process, method, article, or apparatus.

1. A method for controlling warpage of a package strip during curing,the package strip including a plurality of integrated circuit diesencapsulated on a package substrate, the method comprising: clampingedges of the package substrate to hold the package substrate in aposition to decrease cure-induced warpage of the package substrateduring curing of the encapsulant, wherein clamping comprises engaging amajor surface portion of the package substrate near an edge of thepackage substrate with non-zero angled fins disposed at a non-zero angleto the major surface to apply a force to the package substrate to causean initial deformation to the package substrate to counter an expectedcure-induced warpage of the encapsulant on the package substrate; curingthe encapsulant; releasing the edges of the cured package substrate; andpartially curing the encapsulant before clamping the edges of thepackage substrate.
 2. The method of claim 1, further comprising:terminating the application of the force, wherein the terminating isperformed after the curing of the encapsulant.
 3. The method of claim 1further comprising: selecting an angle based on an amount of estimatedcuring warpage.
 4. The method of claim 1 further comprising: measuringan amount of warpage without applying the force; selecting an anglebased on the amount of measured warpage.
 5. The method of claim 1wherein the clamping comprises: supporting the package strip on anon-zero angled land of a package strip carrier assembly; and applying aclamping force to constrain the package strip between the land and anon-zero angled fin.
 6. The method of claim 1 wherein the force isapplied by at least one of rotating a screw, releasing a spring, andactuating a lever.
 7. The method of claim 1, wherein prior to theclamping the edges of the substrate, the method further comprises:placing the package substrate into a carrier having non-zero angledlands which are at a non-zero angle as measured from a horizontal axisthat is substantially parallel with a top or a bottom of the carrier. 8.The method of claim 7, wherein the engaging the major surface portioncomprises engaging the major surface portion of package substrate nearthe edge of the package substrate between a non-zero angled fin and acorresponding non-zero angled land, wherein the corresponding non-zeroangled fin is substantially parallel to the non-zero angled land.
 9. Amethod for controlling warpage of a package strip during curing, thepackage strip including a plurality of integrated circuit diesencapsulated on a package substrate, the method comprising: placing thepackage strip into a package strip carrier assembly, the package stripcarrier assembly having a plurality of non-zero angled lands which aredisposed at a non-zero angle with respect to a horizontal axis that issubstantially parallel to a first major surface of the package strip;clamping edges of the package strip between non-zero angled lands of theplurality of non-zero angled lands and corresponding non-zero angledfins that are substantially parallel to the non-zero angled lands toapply a force to the package substrate to cause an initial deformationto the package substrate to counter an expected cure-induced warpage ofthe encapsulant on the package substrate during curing of theencapsulant; curing the encapsulant; and releasing the edges of thecured package substrate.
 10. The method of claim 9, wherein during theclamping, the non-zero angled lands of the plurality of non-zero angledlands engage the first major surface of the package substrate, and thenon-zero angled fins engage a second major surface of the packagesubstrate, opposite the first major surface.
 11. The method of claim 9further comprising: selecting a non-zero angle for the non-zero angledlands and corresponding non-zero angled fins based on an amount ofestimated curing warpage.
 12. The method of claim 9 further comprising:measuring an amount of warpage without applying the force; selecting anon-zero angle for the non-zero angled lands and corresponding non-zeroangled fins based on the amount of measured warpage.
 13. The method ofclaim 9, wherein the horizontal axis is also substantially paralled to atop or a bottom of the package strip carrier assembly.